Bodily Fluid Blacklight Reveal

"I'm a really friendly ghost!"

Michael: What are all these stains?
Dwight: They're either blood, urine, or semen.
Michael: Oh, God, I hope it's urine.

— The Office (US)

Let's face it: everyone masturbates, but some just are better at hiding it than others. In the case of some people, they tend to get their... reproductive material everywhere, and although it may not seem obvious, the flick of a light switch and a readily available black light will reveal a Jackson Pollockian spermsterpiece, to the disgust and shock of whomever found it.

While semen is the go-to for this trope, blood, urine, feces, etc. can also apply. Their chemical composition, plus the nature of a UV blacklight means that when the lights are off and when a light shines, it will glow.

This trope is usually Played for Laughs, though in police procedurals it tends to be Played for Drama.

Truth in Television: Crime Scene Investigators utilize black lights to locate bodily fluids, including sperm, which happens to glow the brightest due to its chemical composition, although blood requires the use of chemicals, such as Luminol, to make it glow under black lights, and the black lights will also cause lemon juice, many laundry detergents, and toothpastes to glow.

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Examples:

Film — Live Action

• Zig-Zagged in Orphan (2009). John, the husband, becomes suspicious of his adopted daughter, and turns her aquarium's black light onto the paintings in her room. Under the happy, pastoral scenes, the blacklight reveals a series of gory, pornographic images. The daughter (presumably) used invisible ink instead of actual bodily fluids, but the scenes revealed by the light are graphic, to say the least.
• From Guardians of the Galaxy (2014) after Gamora calls the ship dirty:
  Quill: She has no idea. If I had a blacklight, it'd be like a Jackson Pollock painting here!
  Rocket: You've got issues, Quill.
• Early in Scary Movie 2, Dwight, despite being a cripple, is somehow able to perform a blowjob on himself. A few scenes later when the ghost of Hugh Craine is on the loose and everyone has to put on Infra-Red Goggles, Alex looks through her own goggles and can see traces of blacklight around Dwight's mouth, prompting Dwight to ask what she's giggling at.
• In Freaks (2018), ADF agents detect use of Abnormal powers by checking for characteristic blood at the corner of the eyes with UV flashlights. While blood is normally not luminescent under a blacklight without a fluid such as luminol, it's possible that the fluid Abornomals leak when using their powers has a different composition.

Literature

• In Lee Goldberg's novel Mr. Monk and the Dirty Cop (based on the series), Adrian Monk's assistant Natalie Teeger recalls Lt. Disher using a blacklight to show her the amount of fluids in an apparently clean hotel room. After that experience, she is, for once, in agreement with her boss's extreme hypochondria and fear of hotel rooms.
• In The Onion's satirical geography book, Our Dumb World, we have one spot on the map of Hungary (which is pornography-themed) that references this.
  Room looks disgusting under blacklight.
• In The Strain, veteran New York exterminator Vasily Fet always carries a black light to track rats by their urine stains. This proves critical in back-tracing the lair of the vampires who have colonized Manhattan's underground and driven the rats from their usual lairs.

Live-Action TV

• Discussed in Agents of S.H.I.E.L.D. when Hunter asks Fitz if there was a light that could find blood residue.
  Fitz: Not blood.
• The Big Bang Theory: Implied in "The Hawking Excitation". When Howard tells Sheldon to polish his belt buckles in order to get the chance to meet Stephen Hawking, he tells Sheldon to use a blacklight (since the buckles tend to get... splashed... when Howard goes to the urinal). Even worse, he then advises Sheldon not to shine the light around the rest of Howard's bedroom for his own peace of mind.
• Bones: Temperance Brennan carries around a small blacklight to reveal traces of blood at crime scenes, which often reveal where or how someone was murdered.
• Brooklyn Nine-Nine: In "Halloween IV", when the competitors realize something is wrong with the heist, the entire precinct gets switched to blacklight. While this is meant to reveal a secret message on the fake heist plaques, it also has the unintended consequence of showing how filthy the precinct is. Hitchcock and Scully's desks in particular look radioactive compared to the rest of the room.
• CSI: NY: As is true for the entire franchise, investigators use blacklights quite frequently.
  • One of the cases in "Tanglewood" has Danny and Aiden searching for clues in a seedy massage parlor. He aims his light in a waste basket full of used condoms and declares, "This is Chernobyl."
  • In "The Untouchable," Mac and Flack are searching a room in a gentlemen's club for clues after a woman died at a party there. Mac turns on his ALS and finds semen stains on the couch. Flack makes a comment about a different kind of party. Mac says, "Sex isn't illegal, murder is. We need to find blood." He shines his light on the other side of the room and promptly finds cleaned-up blood stains there.
• In an episode of Hotel Hell, Gordon Ramsay makes this point to the owners concerning hotel cleanliness, using black light. In a particularly squalid ill-kept toilet, he is disgusted to reveal it is even on the ceiling. In another episode, he finds suspicious stains all over his room's bedding with the blacklight turned on, prompting this line:
  Gordon: "Ugh, I just touched that! It's like a mosaic of semen!"
• Monk: In "Mr. Monk Goes on Vacation", the hotel detective brings in a machine that can detect traces of many different bodily fluids. When she uses it on Monk's room, it reveals spots all over the place. Completely disgusted, Monk summons housecleaning and orders them to sterilize everything.
• The Office (US): When Michael and Dwight attend a conference, they set up their hotel room for a party, including black lights, and are horrified when they see splatters all over the room when they turn them on.
• In an episode of 1000 Ways to Die, a con artist posing as a health inspector masturbates in a motel room and shows the result to the owner as a way to extort a free room for the night. As the "inspector" sleeps, he left the black light on, which also illuminates the venomous scorpions that are approaching him and eventually sting him to death.
• The show Room Raiders on MTV was an early 2000's dating reality tv show in which a single contestant got to peruse through the bedrooms of three hopefuls to decide which one they would select to date, as the three potential dates watched on from a nearby van. The main contestant had a spy kit that was equipped with tools such as a magnifying glass, tweezers, and a black light. Many a hopeful saw their prospects crushed when their room lit up like a Christmas tree under the UV light.
• In the Saturday Night Live "Bodega Bathroom" musical sketch, two cockroaches sing about how disgusting the bodega toilet is, turning on a blacklight and showing it sprinkled in white.
  All the sticky stuff is fluids
  Want to know for sure? Put a blacklight to it!
• 30 Rock: In Black Light Attack, to see if Liz has been going out with Danny, Jack suddenly turns on a black light while speaking to her and discovers she's covered with marks. He's confused, however, when he finds numerous handprints on the back of her knees, which Liz refuses to explain.
• On Two and a Half Men, CSI agents are exploring Charlie's house after someone dies during a party. When they shine a black light in Charlie's bedroom, they are shocked by the number of stains all over, even on the ceiling. The audience, thankfully, isn't privy to this sight, which one of the agents compares to a Jackson Pollock painting.
• 2 Broke Girls: In "And The Girlfriend Experience", Max and Caroline go to a strip club where they have to convince a woman working there to pose as Han's girlfriend. As she is about to give them a lap dance in the backroom, she switches on the blacklight which reveals sexual fluid all over the couch Caroline and Max are sitting on. Caroline is disgusted while Max is more amused.
  Max: Could you turn the other light back on? [Caroline]'s allergic to the truth.
• The Whitest Kids U' Know: After a dad installs a black light in his son Billy's room, Billy remarks how cool it's going to look with his posters. After his dad shuts off the light, he is greeted by an excessive amount of sperm splotches on the wall. The dad abruptly leaves while the kid ponders aloud why sperm glows.
• In the pilot episode of Touch Me, I'm Karen Taylor on BBC Three, Taylor plays a police detective named Susan who arrives late to a crime scene. The scenes of crime officer asks what took her so long. Susan rebukes that it's four in the morning and she has a social life. The SOCO uses a UV light to look for traces of semen on a bed. He finds none, but he then notices large glowing patches on Susan's face and hair.

Video Games

• PAYDAY 3: In Under The Surphaze, two of the target paintings will be marked with a splatter that only appears up-close. In-universe, this is explained as dried blood getting mixed in with the paint after the artist behind them, Pedro Vicario, attempted suicide whilst working on them.

Webcomics

• Played for Laughs in the xkcd strip "UV", where Megan and Cueball are so horrified and disgusted by what see in their bathroom under a blacklight, they opt for burning their house down, rather than cleaning it up.

Web Video

• Referenced in the Game Grumps playthrough of Doki Doki Literature Club!, when Dan and Arin's player character, FriendArin, apparently prepares for his weekend with Yuri by "scrubbing hardened jizz off of every surface of [his] room," which shows up very brightly under a blacklight.
  Arin: I got one of those luminol sprays and holy shit, it's like Christmas in there.
  Dan: I got a blacklight, and I can see it from space!
• Kurtis Conner: Discussed in his video on the MTV show Room Raiders, in which he was relieved the room-raiding spy kit didn't come with a black light to humiliate the people further. He then parodied it in a sketch, where a girl talks happily about how the boy who owns the bedroom she's in seems perfect, but how she has to try the black-light out to appease the show crew. The black light comes on, and suddenly everything in the room is pure white.
• Natural Habitat Shorts mentions that platypi will glow under UV-light, so one is used as a hotel bellhop during a routine inspection.
  Bellhop: ...why am I blue? Does everyone glow blue? What does blue mean? (Follows the inspector's gaze to the various stains in the room) What does blue mean!?

Western Animation

• Drawn Together: When Toot Braunstein says she wants a baby, she looks for a viable sperm donor through the means of a blacklight. After turning off the lights in the mansion, the room lights up due to the amount of semen. Of particular note, Clara is the only person not covered in semen, Xandir is covered head to toe, even remarking "I'm a really friendly ghost!" and Foxy points to her feet which are completely covered in semen.
• Family Guy:
  • When Carter and Chris go looking for a rare dollar bill, they enter a strip club and ask the bouncer to shut off all the lights except for the black light. When they do, everything is covered in semen, including Connie D'Amico and Tracy Flannigan, as well as most of the dollar bills. Chris remarks how gross it is, with Carter mentioning that the NBA All-Star Game was in town last week.
  • A much more innocuous version occurs when the family temporarily stay in a hotel. Skeptical of its cleanliness, Stewie pulls out a UV light and manages to find a few stains of spittle, semen, and oatmeal. Stewie surmises that "This must be where Wilford Brimley was strangled by Bob Crane."
• Farzar: In Robot Revolution, Zobo the Chaos-elot puts together an elaborate Rube Goldberg-esque chaotic chain reaction at a strip club that includes switching out the venue’s fluorescent lights with black lights. When the manager switches on the lights, they reveal the walls are covered in sperm splotches, to the disgust of everyone.

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